The invention is directed to a device for driving recording carriages and the like, particularly in data recorders, employing a linear motor.
Silent operation is of great importance in such a drive, as well as speed and accurate and exact controllability during step-wise operation and with uniformity, particularly in the application of ink-jet recorders. Previously used drives employed in such applications normally involved a plurality of mechanical components and in the case of data recorders presently in use, the recording carriage preferably is moved, by means of suitable belt or ratchet devices, along suitable guide members which extend in parallel direction with respect to the paper carriage. An arrangement of this type is particularly suitable for the utilization of linear drive means.
Linear motors are known in which a suitable coil or winding support is movable in an air gap under the action of several permanent magnets and in which the current supply to the winding support is effected by means of suitable sliding contacts (German Pat. No. 1,106,855). It is also additionally known to employ a rigid winding support member instead of a flexible support and to move the magnet carrier instead of the winding. However, all of such linear motors employ relatively extended coil windings which are supplied with current over sliding contacts, with the electromotive force acting on such coil to produce a forward thrust which is operable upon the coil with the cooperation of suitable mechanical devices, whereby the coil structure is substantially the equivalent to the drive structures previously described in connection with data recorders. Consequently, this type of device does not offer any great advantages, as compared to the described previously used drives, as a result of the relatively great masses which must be accelerated.
A teleprinter drive employing a linear electromotor is known from Offenlegungsschrift No. 2,126,481 in which, for the production of the desired magnetic field, a permanent magnet is disposed between two parallel plates which are connected over a magnetic bridge. However, the production of the necessary magnetic field by means of a relatively long elongated permanent magnet presents considerable disadvantages with respect to the control of the electromotive forces in the driving coil. It will be appreciated that the manufacture of uniformly magnetized plates which extend over a large area is, in particular, technically difficult. Due to the required field strength distribution, the magnetic plates in such an arrangement cannot be extended to the edge of the ferromagnetic rails whereby considerable stray fields result, particularly at the edges. The alternative utilization of electromagnets also is not practical as it is difficult to produce a sufficiently exact gap variation in the magnetic field, in order to produce, for example, a space dependent force, i.e., a force varying with the field gap. The disposition of the magnetic field in the air gap requires a relatively large dimensioning of the entire structure and consequently results in greater weight.